a. Field of Invention
The invention relates to aircraft flight-control systems and, more particularly, to a computer-assisted propulsion control system that enables a pilot to land a plane safely when its normal control surfaces such as elevators, rudders, and ailerons are disabled.
b. Background of the Invention
Aircraft flight-control systems are designed with redundancy to ensure low probability of failure. Nevertheless, there have been several instances of major flight-control-system failures. In these situations engine thrust becomes the last remaining mode of flight control. It is possible for pilots to control an aircraft using thrust by manually moving the throttles to maintain or change flight path and heading angles. However, this places a high work load on the pilots which may result in a crash and loss of life. The challenge lies in creating a means of sufficient degree of thrust-modulation control to safely fly and land a stricken airplane without causing a high pilot workload.
Propulsion Controlled Aircraft (PCA) is a computer-assisted engine control system that enables a pilot to land a plane safely when its normal control surfaces such as elevators, rudders, and ailerons are disabled. PCA is a damage mitigation technology that utilizes propulsive thrust for aircraft control in the event of partial or total loss of flight controls due to any failure including loss of hydraulics. Whether used in military or commercial aircraft, PCA has the potential to reduce the number of aircraft accidents due to loss of flight controls.
In the recent past, a PCA system has been developed and disclosed in U.S. Pat. No. 5,330,131 by Frank W. Burcham et al. (incorporated herein by this reference) based upon a program modification of an otherwise normal Flight Control Computer (FCC) that, in the event of a failure of the normal flight control system of a multiengine airplane, substitutes normal pitch axis control with symmetric control of the engines through their FCC driven servos using pitch attitude and pitch rate sensed by gyros to provide the feedback signals necessary to track a pitch command signal. That patented flight control system requires extensive modification not only of the FCC but also of each full-authority digital engine control (FADEC) computer for each engine.
More recently U.S. Pat. No. 6,041,273 to Burken et al. issued Mar. 21, 2000 disclosed an emergency control aircraft system using thrust modulation that compares the input flight path angle signal from a pilot thumbwheel with a sensed flight path angle to produce an error signal, an ultimately, an aircraft thrust control signal to drive a throttle servo for all engines. This effectively serves as an emergency backup system for a PCA that requires only program modification of the FCC without any changes in engine computers.
U.S. Pat. No. 6,126,111 to Burcham et al. issued Oct. 3, 2000 shows a further refinement to the foregoing emergency flight control system that additionally uses lateral fuel transfer to allow a pilot to regain control over an aircraft under emergency conditions. Here, where aircraft propulsion is available only through engines on one side of the aircraft, lateral fuel transfer provides the means by which the center of gravity of the aircraft can be moved over to the wing associated with the operating engine, thus inducing a moment that balances the moment from the remaining engine, allowing the pilot to regain control over the aircraft.
Unfortunately, all of the foregoing and all other known current implementations of PCA require expensive modifications to aircraft software and hardware as well as recertification of the aircraft. It would be greatly advantageous to provide a PCA capability at a fraction of the cost of full implementation for widespread commercial and military deployment.